In spite of the serious threats of intentional or accidental exposures to radiation, molecular mechanisms of injury after total body irradiation (TBI) are not completely clear, hence radiomitigative approaches remain insufficient. Our discoveries of oxygenated cardiolipins (CLs) as required stages of TBI apoptosis have already resulted in mitochondria-targeted GS-nitroxides and imidazole-substituted fatty acids as anti-apoptotic radiomitigators. Similarly, deciphering the TBI ferroptotic signaling by hydroperoxy-phosphatidylethanolamines (HOO-PEs) produced by 15- lipoxygenases (15LOX) complexes with phosphatidylethanolamine-binding protein 1 (15-LOX/PEBP1) guides us to new inhibitors as novel radiomitigators. Our demonstration of ?theft- ferroptosis? by a bacterial pathogen, Pseudomonas aeruginosa, utilizing its 15-LOX (pLoxA) (12) to trigger ferroptosis of the host (epithelial) cells indicates that TBI induced non-sterile inflammation may be also therapeutically targeted. Our central hypothesis is that radiation triggered responses engage several types of programmed necrotic death, particularly ferroptosis, in GI epithelial cells and the major innate immune cells, neutrophils and macrophages, evolving over time and driving necro-inflammatory vs pro-resolving apoptotic responses during sterile and non-sterile inflammation and culminating in multiple organ dysfunction and mortality. This sets the stage for a principally new understanding of the TBI mechanisms and leads to a new harmonized radiomitigation strategy of time- and mechanism-specific targeting of the leading cell death pathways. Our hypothesis will be tested as follows: Aim 1: By employing Redox Lipidomics identify specific oxygenated phospholipid signatures of the major death programs in epithelial cells, neutrophils and macrophages of the GI of irradiated mice at different stages of sterile and non-sterile necro-inflammation. These newly discovered TBI lipid biomarkers will be related to: i) specific protein markers of cell death, ii) major pro- and anti-inflammatory lipid mediators, iii) cytokines, and iv) breach of the epithelial barrier and immunosuppression. Aim 2: Explore molecular mechanisms of sensitivity/resistance to ferroptosis of macrophages and neutrophils polarized to M1 (N1) and M2 (N2) states in response to pro-/anti-inflammatory conditions and expression of 15LOX and iNOS/NO? system in vitro and TBI induced ferroptosis in vivo. We will employ 15LOX and iNOS KO mice and also quantitatively assess the role of P. aeruginosa and its pLoxA in gut ferroptosis and radiosensitivity of mice to TBI. Aim 3: Design new selective inhibitors of pro-ferroptotic catalytic activity of mammalian 15LOX as well as prokaryotic pLoxA of P. aeruginosa and test them as anti-ferroptotic radiomitigators during sterile and non-sterile stages of TBI radiation disease. Overall, this project is based on an entirely new concept that abandons the search for a single ?silver-bullet? radiomitigator and includes a harmonized combination of several mitigators controlling TBI triggered aberrant reactions in time- and mechanism-dependent manner.